Like any profession, marketing has a roster of marquee names – the individuals considered trailblazers in the industry. Some created legendary advertising campaigns or slogans; others founded global agencies. Still others developed philosophies that were widely adopted and are still taught in business and marketing degree programs decades later.

Let’s take a closer look at just three of marketing’s big-hitters:

Leo Burnett

Born at the end of the 19th century, Leo Burnett eventually founded the Chicago-based advertising agency that today has offices around the globe and still bears his name more than 40 years after his death. Burnett and his agency were responsible for creating some of the world’s most famous product icons, including the Pillsbury Doughboy, Tony the Tiger and the Marlboro Man.

Burnett put a premium on visuals over words, believing that images appealed more directly to human emotions and consumers’ instincts. Today, the growing use of infographics and photo-sharing platforms like Pinterest and Instagram in marketing campaigns appears to support Burnett’s views on the power of visuals.

Mary Kay Ash

Mary Kay Ash, better known as simply Mary Kay, was a young mother when she began her career selling household products door-to-door in the 1930s. When she retired from direct sales three decades later, she used her life savings of $5,000 to launch the skin care and beauty products company that eventually would make her a household name.

From a small storefront location in Dallas, Texas, the company has grown to include more than 2 million independent beauty consultants in more than 30 nations and annual wholesale sales exceeding $3 billion.

Ash developed a theory of sales and marketing that emphasized the importance of valuing and recognizing others, including employees and customers. Indeed, the pink Cadillacs awarded to the company’s top performers have become a symbol of the company itself.

David Ogilvy

Before founding the New York-based ad agency Hewitt, Ogilvy, Benson & Mather in 1948, David Ogilvy had worked an assortment of jobs, including selling stoves door-to-door and conducting research for the Gallup organization. Ogilvy, who was born in England and immigrated to the United States shortly before World War II, had even spent a few years as a farmer. But he did not have a marketing degree or any training as a copywriter.

Still, his ad company hit the ground running, securing accounts with major players such as Shell, American Express and General Foods. “I doubt whether any copywriter has ever had so many winners in such a short period of time,” Ogilvy wrote in his autobiography.

By the mid-1960s, the agency had evolved from a two-employee operation into an international company known as Ogilvy & Mather, and had also become one of the first advertising firms to be publicly traded. Today, it has more than 400 offices worldwide.

One of Ogilvy’s best-known campaigns was for luxury carmaker Rolls-Royce, which included the ad copy: “At 60 miles an hour, the loudest noise in this new Rolls-Royce comes from the electric clock.”

Considered 20th century giants of the marketing world, Ogilvy, Ash and Burnett shared similar traits, including a focus on quality, and a willingness to follow their instincts and think big.